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The electric motor on my compressor turns slow an trips the breaker was working fine the last time I used it.

by gary
(Ponca City, OK.)

33 gal. 11.9cfm. craftmans. A.O.smith motor. 115V rpm3450 mod. 919.167340. motor turns slow then trips breaker work fine last time it was used. how many ohms should this motor show on meter. ITs showing 3

I don’t have the spec for that, Gary.

If you go to and input your model number, you can see the parts diagram and parts list.

You can also (if during business hours) chat on line with them. I would ask if that info was in the manual before I ordered one, or, just if they knew what that was.

What is the pressure in the tank when “motor turns slow then trips breaker”? On cut in with pressure, or even when the tank is empty?

If no change in the power supply to the compressor, then check the intake filter to make sure it’s clean, pull the line from the pump head to the tank and see if the compressor runs OK then. If so, apply gloved back pressure to the fitting or port in the pump head to see if this causes the motor to lug. If not, pull and clean the check valve, then try it again.

220v 2.2kw capacitor start, capacitor run motor, runs slow and overheats

by Frank Duffin
(Cardiff, Wales, UK)

Compressor motor terminal wiring

Got this motor to run a hydraulic press. Even when not connected to press the following happens:

Motor starts up really slow, the cable (16 amp) starts to heat up from the plug end. If left on for more than a minute the motor starts to heat up.

It is a 220v motor single phase.

Was working before being posted to me, it was taken to 2500psi where it stalled the pump.

I am certain the supplier is correct and it was ok before posting.

The plug is connected to a 30amp main fuse in my house. It blew a 13amp fuse before I changed the fuse to 20amp. I am wondering if the problem is the start capacitor/run capacitor or the changeover switch?

I am just using a normal switch, ie no soft start, DOL etc. My research suggests that this motor should run on a normal 220v household supply, albeit linked to a 16amp + fuse.

The connection box has four connections, U1, U2, 3 and 4. My live is connected to U1, neutral to U2.

Just replaced brushes and put it back together – Running Problems

I have a CFBN 125A-3 I just replaced brushes and put it back together and it stutter runs.

I mean it runs and turns off over and over as though someone is plugging it in and out. Can You Help?

Friend, it seems clear to me that if the problem didn’t exist before your re & re the motor, and now the problem is there, it is something you did or didn’t do on the rebuild.

I hope someone that rebuilds electric motors reads this and can offer some guidance.

Air compressor motor stops

by Terance W. Cooley, Sr.
(Ankeny, Iowa USA)

after I push the reset (red) button, the compressor will run for about 5 seconds and then cut off. The air tank is not full at all of air.

Sounds like motor is failing, or you haven’t enough current to the motor to allow it to run properly.

The reset button is often a thermal reset. The cut off occurs when the motor gets to hot, to try and save it from heat related damage. By repeatedly pushing the thermal reset, and not addressing the issue that caused it, you are likely doing more damage to the motor.

Make sure nothing else is pulling power from the same circuit that feeds your compressor. If, after that, the symptom continues, I’m guessing that your motor is the problem.

My Air Compressor Runs for a bit then starts to shake and turns off. Too hot?

I have a SMC Vertical Air compressor. The compressor will start to run for a bit then it starts to shake quite a bit then throws the breaker on the electric motor of the compressor it’s self. Any information would be a great help


G’day, Steve. So, it runs for a bit… hmmmm? How long is that? Are we talking a couple of seconds, or couple of minutes, or somewhere in between? When it’s running for a bit, are you seeing a pressure increase in the tank?

What starts to shake… the whole compressor, the motor, can you identify the item that’s causing the shaking? In order for more-than-usual vibration to occur, something has let go.

I don’t know your exact compressor, partially because you don’t indicate the model, and mostly because there are eighty seven gazillion makes and models and I’d sure like to meet the person that could remember them all.

If there are motor mounts, check these. If there are any elastomeric mounts where the whole compressor pump and motor assembly are attached to the mounting plate, check these. Compressors vibrate like stink, and it’s usually a soft, elastomere that absorbs the oscillation so that your compressor doesn’t dance across the room like Fred Astaire on drugs. If you don’t know who he is, don’t sweat it. It just shows how old I am.

As to it’s shutting off, I don’t know at what pressure that occurs, so is it going of on normal cut out, or is the vibration, perhaps, causing the pressure switch to trip off prematurely?

Comment by Al: Seeing that it drops out the circuit breaker on the motor! You have an excess load or a faulty motor. As you said you had the tank pipe disconnected! – Regards, Al ( elec fitter/tools specialist)

Comment by Steve I have further diagnosed the compressor. It seems if I take the line that feeds the air compressor tank of the pump. With the pump line attached to the tank it never starts to build pressure and only runs for about 2 minutes then shakes quite a bit. I have need around quite a few compressors and ever see one shake like this one.

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